The present invention relates to sensors utilized in vehicle service procedures, and in particular, to the improvement of traditional vehicle alignment angle sensors and moving vehicle service components by the incorporation of micromechanical accelerometers and gyroscopes.
During vehicle service procedures, the measurement of angles and angular changes associated with vehicle components and vehicle service devices, such as vehicle lifts, is critical. On a vehicle, the measurement of the alignment angles of the vehicle wheels is critical to vehicle handling, performance, and fuel economy. On vehicle service devices, such as vehicle lift rack systems, the measurement of the angular alignment between left and right vehicle supporting runways, as well as the angular orientation of lifting components is critical to determine if the surface on which a vehicle is disposed is level and/or the height at which the vehicle has been elevated.
Various systems have been designed to facilitate the measurement and alteration of the principle vehicle wheel alignment angles on automotive vehicles such as light trucks and passenger cars. Principle wheel alignment angles include the toe angle, which generally corresponds to the direction in which a wheel is pointing, and the camber angle, which corresponds to the inward (negative) or outward (positive) tilt of the wheel relative to a vertical center plane of the vehicle. Procedures and methods by which additional vehicle wheel alignment angles such as caster and steering axis inclination (SAI) can be determined from measurements of the wheel toe angles and camber alignment angles are well known, and are described in SAE Publication 850219 to January, entitled “Steering Geometry and Caster Measurement”.
In one type of vehicle wheel alignment system, sensors units configured for measuring vehicle wheel angles are removably mounted to the individual vehicle wheels. For example, U.S. Reissue Pat. No. 33,144 to Hunter et al. and U.S. Pat. No. 4,319,838 to Grossman et al. each describe a vehicle wheel alignment system for vehicles having two axles which use cooperative pairs of electro-optical transducers removably mounted to the vehicle wheels to determine the toe alignment angles of each wheel of a vehicle. A typical arrangement of alignment angle sensors for a two-axle vehicle includes either six or eight toe alignment angle transducers carried by support assemblies removably mounted to the vehicle wheels, two on each steered (front) vehicle wheel, and one or two on each fixed (rear) wheel. The '144 and '838 patents illustrate the geometry of this arrangement and the various wheel alignment angles which can be measured or computed.
Typically, in a six-sensor configuration, a first electro-optical toe angle sensor associated with a front wheel is disposed on an arm extended from a transducer housing coupled to the vehicle wheel. The toe sensor disposed on the arm functions in cooperative relationship across the front of the vehicle with a corresponding sensor on the opposite side of the vehicle. A second electro-optical toe angle sensor disposed in the transducer housing functions in cooperative relationship with a corresponding electro-optical toe angle sensor disposed in a transducer housing removably mounted on a rear wheel on the same side of the vehicle. Optionally, in an eight sensor configuration, a second electro-optical toe sensor associated with the vehicle's rear wheel is disposed on an arm extended from the transducer housing to function in cooperative relationship across the rear of the vehicle with a corresponding sensor on the opposite side of the vehicle.
To obtain a measurement of a vehicle wheel camber angle, U.S. Pat. No. 4,879,670 to Colarelli describes the use of a commonly utilized gravity-referenced accelerometer/inclinometer which is removably mounted to a vehicle wheel. The use of a gravity-referenced accelerometer/inclinometer to measure the camber angle of a vehicle wheel assumes that the vehicle is stationary and disposed on a surface which is level and flat. If the vehicle is disposed on a vehicle lift system during the procedure, the runways of the vehicle lift system may be inclined with respect to each other or to a horizontal plane, possibly resulting in miscalculation of the proper vehicle wheel alignment angles.
While the '670 Colarelli reference describes the use of a force balanced tilt sensor and associated electronics, alternative commonly utilized designs may utilize electrolytic fluid-based tilt sensors and associated electronics. Typically, one or more gravity-referenced accelerometers/inclinometers are incorporated into the transducer housings or support assemblies mounted to the vehicle wheels, together with the various electro-optical toe angle transducers, power sources, and associated communication and logic circuits.
Exemplary commonly utilized vehicle wheel alignment transducers incorporating gravity-referenced angle sensors and electro-optical toe angle sensors are the DSP500 Series Sensors manufactured by Hunter Engineering Company of Bridgeton, Mo. for use with one of several vehicle wheel alignment console units. Individual transducers removably mounted to the vehicle wheels may communicate with each other, and with a wheel alignment console unit, either via communication cables or wireless transceivers.
An alternative type of commonly utilized vehicle wheel alignment angle measurement system acquires information related to the position and orientation of individual vehicle wheels in three dimensional space utilizing a optical targets and cameras. For example, as is shown in U.S. Pat. No. 5,675,515 to January, predetermined optical targets may be removably coupled to each wheel of the vehicle, and images of the optical targets acquired by cameras coupled to a vehicle wheel alignment console unit. By processing the acquired images, the position and orientation of each optical target (i.e., pitch, yaw, and roll) can be determined in a three-dimensional space, from which individual vehicle wheel alignment angle values can be calculated in a common coordinate reference system.
Both types of commonly utilized vehicle wheel alignment angle sensor systems suffer from several drawbacks. Wheel-mounted transducer housings incorporating electro-optical toe angle sensors and camber angle inclinometers are bulky units which are susceptible to damage from shock or impact, and require awkward extension arms to enable line-of-sight communication across either the front or rear of the vehicle during toe angle measurement procedures. Camera-based vehicle wheel alignment systems often require larger or dedicated service bays due to the distances which must be maintained between the camera and the optical targets. These system often require a permanent installation or mounting of the cameras and are typically not portable from one service bay to another.
Accordingly, it would be advantageous to provide an improved vehicle wheel alignment angle sensor system to which can replace or supplement commonly utilized vehicle wheel alignment angle sensors, which does not require bulky and awkward extension arms for toe angle measurement, and which has a reduced sensitivity to shock, impact damage, and dirty operating environments, but which are easily portable from one service location to another.
It would be further advantageous to improve or enhance existing vehicle service devices, such as vehicle lift systems or alignment systems, through the use of low-cost, compact and durable inclinometers and accelerometers to provide position and orientation information associated with moving components of the vehicle service devices or vehicle frame and body components.